New water-based technique bonds III-nitride thin films to diamond substrates

Group III-nitride materials, including aluminum nitride, gallium nitride and indium nitride, are grown as thin films and used as semiconductors in LEDs, sensors, solar cells and more. Common techniques bond these thin films to different substrates by adding metallic, dielectric, or polymeric layers in between the thin film and bond substrate. However, the added layers may have unfavorable properties, such as being electrically conductive, thermally insulating, or mechanically soft. This can degrade the performance of the bond substrates, and ultimately of the device.

Gerrer et al. introduce a new, simple bond technique for III-nitride thin films without the need for extra layers between the thin film and bond substrate, which can potentially outperform other bond technologies electrically, thermally, and mechanically.

The authors chemically reconstructed the surface of a III-nitride thin film to bond it to diamond, which dissipates heat and improves device performance when used as a bond substrate for thin film electronics. By adding a very thin layer of water in between the AlN surface layer of an AlGaN/GaN heterostructure and a single or polycrystalline diamond substrate, the AlN surface layer of the heterostructure transforms into a solid aluminum hydroxide bond layer with a thickness of 30 nm.

Author Thomas Gerrer said that their bonding technique offers a new degree of freedom to the fabrication of high-power, high-frequency III-nitride thin film electronics. Heat generation, much of which comes from the transition layers of the thin film and the substrate, hinders the performance of these devices. The new bonding technique, combined with a process that could remove or reduce the thickness of the transition layers to aid heat dissipation, may improve future device performance.

Source: “Adaptive low-temperature covalent bonding of III-nitride thin-films by extremely thin water interlayers,” by Thomas Gerrer, Andreas Graff, Michél Simon-Najasek, Heiko Czap, Thomas Maier, Fouad Benkhelifa, Stefan Müller, Christoph Nebel, Patrick Waltereit, Rüdiger Quay, and Volker Cimalla, Applied Physics Letters (2019). The article can be accessed at https://doi.org/10.1063/1.5095816 .